1. Field of the Invention
The invention relates generally to electrical connectors and, more particularly, to a method for assembling a controlled impedance electrical connector using conventional components.
2. The Prior Art
Electrical signals operating at very high frequencies require controlled impedance and energy containment in their associated wiring and connectors. Commonly, controlled impedance and energy containment is effected by using shielded or coaxial cable and/or special electrical connectors or connector inserts. Such connectors typically are custom-made for particular applications and, therefore, often are expensive and not readily available when needed.
It would be beneficial to provide a method for fabricating a controlled impedance connector for a variety of applications using readily available, conventional components.
The present invention provides a novel method for assembling a controlled impedance electrical connector, such as the connector disclosed in co-pending U.S. patent application Ser. No. 09/607,487. More particularly, the present invention provides a method for assembling a controlled impedance electrical connector using conventional connector components, including conventional connector shells and inserts. The method of the present invention can be used in connection with connector shells having nearly any cross-section, including, without limitation, circular, square, and rectangular. The method of the present invention can be used to assemble an impedance controlled connector for use with conductors carrying a variety of signals, including single-ended signals, differential signals, and bidirectional differential signals. Test results indicate that a controlled impedance electrical connector assembled using the process of the present invention provides appropriate energy containment for signals varying in frequency from direct current (DC) to approximately 3.5 GHz.
In a preferred embodiment, the method of the present invention can be used to terminate an impedance controlled cable, such as a cable having a center conductor and a surrounding shielding braid, to a conventional insert in a conventional electrical connector shell. Preferably, the impedance controlled cable is prepared for termination by first stripping a length of outer jacket away from an end of the impedance controlled cable, leaving all but a short length of the underlying shielding braid in place. The exposed shielding braid then can be pushed back against the end of the remaining outer jacket, exposing the inner dielectric insulation. A short length of the inner dielectric insulation (and center conductor protective wrap, if present) is removed to expose the center conductor. Preferably, the center conductor is folded back upon itself to provide an adequate diameter for crimping.
In a preferred embodiment, a standard M39029/56-348 connector socket or M39029/58-360 connector pin (or the respective, suitable alternative) then is crimped onto the center conductor using a conventional crimping tool and die. A small section of shrinkable tubing can be installed across the gap between the crimp contact, i.e., the connector socket or connector pin, and the inner dielectric insulation to provide additional mechanical strength to the connection.
The shielding braid then is replaced over the inner dielectric insulation. Preferably, the shielding braid is spread evenly over the inner dielectric insulation, ensuring that no opening in the braid has a dimension larger than {fraction (1/20)} of a wavelength corresponding to the highest frequency to be handled by the connector (or, in a time domain, {fraction (1/20)} of the fastest transition speed of a signal, as would be known to one skilled in the art). A wire can be wrapped around the braid to cover any opening of excessive size. If such a cover wire is used, it preferably is soldered to the shielding braid to improve the overall shielding characteristic and to hold the wire in place, thus ensuring the opening remains covered. A drain wire preferably is added around the shielding braid near the end of the outer cable jacket and soldered in place.
The foregoing steps describe the preferred method for preparing a cable carrying a single-ended signal for termination at a connector insert. The method of the present invention also can be used in connection with, for example, multiple cables or a multi-wire cable carrying differential signals and bidirectional differential signals, among others. In a differential signal application, a second cable or wire is prepared and terminated in the same manner as for the single-ended signal application described above. The drain wires of the two cables or wires then are twisted and preferably soldered together. A standard M39029/56-348 connector socket or M39029/58-360 connector pin (or the respective, suitable alternative) is crimped onto the twisted and soldered drain wires using conventional tools. In a bidirectional differential signal application, a second pair of cables or wires for the second signal path also is prepared, as described above.
The prepared cables and/or wires are arranged into a predetermined pattern in which they will be configured when installed into the connector. This pattern is selected to ensure that the assembled connector will exhibit adequate impedance control characteristics. This pattern can be determined using any suitable parameter extraction software, such as the Maxwell(copyright) program available from the Ansoft Corporation of Pittsburgh, Pa., or other commercial or proprietary program. One suitable alternative software package is available from Innoveda of Redmond, W.Va.
The prepared and arranged wires are inserted into a conventional insert in a conventional connector housing in the predetermined pattern. Preferably, all of the conductor termination components (i.e., connector sockets or pins) associated with a particular cable or group of cables are pressed into the connector insert substantially simultaneously, a little bit at a time, to avoid placing excessive strain on any of the wiring. Any practical number of conductors can be prepared for and terminated at a connector in the foregoing manner. Once installed into a connector, individual connector sockets and/or pins can be removed and reinserted using conventional insertion and removal tools.
If reference planes are needed for impedance control within the connector, as would be known to those skilled in the art, they may be provided by inserting signal pins into the connector insert in a predetermined configuration and grounding them to the connector shell, thus forming a Faraday Cage around the signal wires requiring such impedance control measures. Preferably, the grounds (or drains) of the relevant signal wires are connected to any of these grounded pins.
Overall shielding of the cable also can be accomplished using conventional connector fittings in a novel manner. More particularly, the shielding can be bunched at the location where the shielding normally ends. This allows the shield to continue within the connector to provide impedance control right up to the inner face of the connector housing.